Computer Simulation of H2 Effects on Electrochemical Corrosion Potential in the Reactor Coolant Circuit of Pressurized Water Reactors

摘要

A model for the electrochemical properties of the primary coolant circuit of a PWR, P-ECP, has been developed to calculate the concentrations of water radiolysis products, including O2, H2O2, OH, O2-, HO2, H, H2, etc, using a proven radiolysis model, and to estimate the electrochemical corrosion potential (ECP), using a Mixed Potential Model that incorporates experimentally measured kinetic data for the hydrogen electrode reaction (HER). At all points around the primary coolant circuit of a PWR. The calculations have been carried out as a function of the hydrogen added to the coolant over the range of 1 ppm to 80 ppm. The modeling shows that the ECP in the hot leg and the cold leg of the steam generator tubes is displaced sharply in the negative direction with increasing hydrogen concentration to values that are more negative than the critical potential for the occurrence of hydrogen-induced cracking in Alloy 600 in PWR primary environments, particularly for high hydrogen concentrations. Therefore, we conclude that high hydrogen levels are potentially deleterious to the integrity of the steam generator tubes and this fact should be interpreted in terms of the need to devise a water chemistry that recognizes the need to maintain the corrosion potential (ECP) at an appropriate value to avoid HIC of Alloy 600 steam generator tubes. The current coordinated water chemistry recommended by EPRI fails to do this.